Hypothalamic co-localization of substance P receptor and transneuronal tracer from the lordosis-relevant lumbar epaxial muscles in the female rat.

Previous studies indicated that within the ventromedial hypothalamus (VMH), the estrogen receptor α (ERα)-containing neurons express substance P (SP), but do not comprise the majority of projection neurons. The present study tested the hypothesis that projection neurons within the VMH express SP receptors (NK1), allowing responsiveness to signals from ERα-containing neurons. Pseudorabies virus was transneuronally transported from the lordosis-relevant lumbar epaxial muscles to the VMH, labeling 28% of the NK1-containing neurons in the VMH and surrounding area. Thus, SP may influence sexual behavior through its release from the ERα-containing neurons, perhaps synaptically affecting NK1 receptor-labeled lordosis-relevant projection neurons within the VMH.